The invention relates generally to semiconductor devices and, more particularly, to stacked die semiconductor devices and to methods for uniquely identifying individual die within a stacked die structure.
Semiconductor devices are generally constructed from silicon or gallium arsenide wafers through a fabrication process that involves a number of deposition, masking, diffusion, etching, and implanting steps. Each fabrication run results in a wafer with a number of identical integrated circuit (“IC”) devices formed therein. After fabrication, the wafer is separated into individual units or die, where each die includes one IC device. Traditionally, individual die are encased in a molding and electrically connected to leads that protrude therefrom. More recently, multiple die have been arranged within a single enclosure. In one such arrangement, two or more die are aligned vertically and electrically interconnected to form a single component. Components formed in this manner are said to employ stacked die or a stacked die structure.
Stacked die structures permit design engineers to increase a system's circuit density—the amount of circuitry per unit area of printed circuit board. Within a stacked die structure, however, it can be important that die are individually selectable. For example, when multiple memory circuit die are stacked to form a single memory component, it can be important that each die be individually activated or selected. In the past, this capability has been provided by remapping various control pins such as chip select and/or clock enable pins from each die within a stack through the use of fuses, anti-fuses and redistribution layers (“RDL”). While these approaches have proven successful, they require that die destined for a first position (e.g., the bottom-most die in a stack) be processed differently from a die destined for a second position (e.g., the top-most die in a stack). In addition to the added cost of processing die in this manner, each die that is different from another die must be segregated and tracked uniquely via a manufacturing parts tracking system, further adding to the cost of conventional stacked die devices. Thus, it would be beneficial to provide improved stacked die structures that utilize dies fabricated in a consistent manner and wherein such die would be capable of automatically sensing their position in a stacked die structure such that they are individually and uniquely selectable.